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From: legg@magma.ca (R.Legg)
Newsgroups: sci.electronics.design
Subject: Re: Comparator snap on-off ??
Date: 16 Oct 2002 15:04:57 -0700
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NNTP-Posting-Date: 16 Oct 2002 22:04:58 GMT
> I understand that the circuit requires hysteresis to function better
> and I have tried to apply it to the circuit. Applying it to the
> inverting input section works fine but when I try to apply it to the
> non-inverting input also it messes the inverting section up. The
> reference levels are provided by a resistor divider network and trim
> pots for fine adjustment. The input signal is provided by the ouptput
> stage of an op-amp that amplifies the thermistor being monitored. The
> level changes very slowly and as such causes oscillation at the
> transition points. What I am ultimately trying to find out is: How can
> I apply hysteresis to both sections at the smae time without
> interaction between the two?? Everything I have tried so far makes one
> section work as desired but not the other. Any ideas ??
>
> http://flubbster.tripod.com/comp_circuit.jpg
Mike,
The hyterisis components can work at much higher impedance levels than
the actual voltage divider if you place a resistor in series with the
relevent IC input pin. Develop your millivolt hysterisis across this
resistor.
Because the circuits switch at different voltages, there shouldn't be
much interplay between the two.
You have to include the static hysterisis voltage in your setpoint
calculations, as it will seldom be symetrical about the original
calculated set points, depending on the output switch's compliance.
RL